Electric induction furnace



Jan. 5, 1932. E. F. NORTHRUP ELECTRIC INDUCTION FURNACE Filed llaich 2a,1930 2 Sheets-Sheet 'llllII/IIIIll/I/ fllllllllllllllll .IIIIIIIIIIIIIIJan. 5, 1932. E. F. NORTHRUP ELECTRIC INDUCTION FURNACE Filed March 26,1930 2 Sheets-Sheet 2 Patented Jan. 5, 1 932 UNITED STATES PATENT OFFICExnwm rrrcn 1103mm, or rnmcn'rou, NEW mam, assreuon 'ro aux mmcrno-THER'MIO CORPORATION, 01? JERSEY AJAX PARK, NEW JERSEY, A CORPORATION 01m ELEUI'BIC INDUCTION FURNACE 'Applicatlon filed Iarah 28, 1980'. SerialIo. 438,887.

My invention relates to methods and apparatus for the control ofstirring in a coreless induction furnace.

A purpose of my invention is to concentrate the number of ampere turnsper unit axial dimension applied to one portion of the charge withrespect to that a plied to another portion of the charge, an so regulatethe stirringin the charge. Y

A further purpow is to grade the inductor coil of an induction furnace,and to utilize the graded coil to control the stirring of the charge.

A furthero purpose is to concentrate the number of inductor coil turnsat either or both extremities of the coil and to selectively control thestirring in the charge by the use of an inductor coil so graded asdesired.

A further purpose is to space from center to center certains turns of acontinuous conductor forming an inductor coil relatively closely withrespect to the spacing of other turns of the same inductor.

. A further purpose is to form an inductor coil'of hollow water-cooledtubing, and to flatten the tubing parallelto the coil axis where theturns are to be spaced close together, transversely to the axis wherethe turns are to be spaced far apart, and to leave the tubing round orpartially flattened 'as desired with progressive or abrupt transitionsbetween these two extremes. Further purposes will appear in thespecification and in the claims.

. I intend the present application to include number of turns per unitof axial dimension is increased at one point along the II with respectto that at another point. e point of high concentration is arbitrarilyreferred to by me as the point toward which the coil is graded.

typesofin uctorcoil.

Ordinarily in inductor coils according to my invention the number ofturns, r unit axial dimension between any two ar itrarily chosen pointswill progressively change from that in the neighborhood of one point tothat in the neighborhod of the other pint.

It has previously been proposed to control the stirring in a corelessinduction furnace by physically elevating or lowering the inductor coil.This I consider undesirable at times because of the mechanism r uired.It has further been suggested that t e inductor coil be provided withtaps, and the power current be connected selectivel taps at a chosenheig t on the furnace .in

order to regulate the stirring. This structure is limited in utilitybecause the idle portions of the inductor coil will be heated by theflux from the live portions of the coil, thus wasting energy and coolingcapacity. Further more, tapping the coil is expensive and sometimes nototherwise wholly satisfactory.

Stirring in the coreless induction furnace is due to the combined actionupon the charge .of motor effect of the inducing current upon the chargecarrying the induced current and pinch effect of the secondarycurrentfilaments upon each other. In both cases, the

stirring produced is proportional to the square of the number of ampereturns per unit axial dimension in the inductor coil. I have discoveredthat by concentrating a high number of ampere turns per unit axialdimension at one point alon the inductor coil, and-nsin a lower number 0ampere turns per unit axi dimension in other parts of the coil, I mayproduce very fyzlr-l'olrxlounced effects upon the stirring in the ace.

Stated in another'way, I find that chan in theefiective center ofgravity of the mductor coil with r to the center of gravity of thecharge tend to afiect the stirring in the charge in a very pronouncedmanner.

For the of clear illustration of my invention I have chosen toshow a fewforms only in the drawings. 7

Figures 1, 2 and 3 are dia atic sectionsof m ace provided with variousto any two of the.

Figures 4 and 5 are axial sections showing slightly di ferent forms ofmy invention suited forwater-cooling.

Like numerals refer to like parts throughout.

Referring to Figures 1 to 3, the same furnace and circuit connectionsappear throughout. I show an inductor coil 15 supplied with current froma conventional source 16 through lines 17 and 18. The power factor maybe very desirably corrected, as for example by the condenser shown at19.

The crucible 20 holds a charge 21 which in the illustrations is assumedto be molten.

In Figure 1 the inductor coil is graded (i. e., has its turns closertogether from the center of one to the center of the next) from thepoint 22 of low concentration at the bottom of the coil to the oint 23of high concentration at the top of t e coil.

The spacing of the turns intermediate between these points of low and hih concentra tions varies progressively from t emaximum spacing in mymost desirable form.

While progressive grading is desirable, it is not necessary, andadvantage might be obtained from my invention by passing abruptly from apoint of low turn concentration to a point of high concentration, or bychanging the intermediate spacing according to any desired law,arithmetical or geometrical.

Since in Figure 1 the number of ampere turns per unit axial dimension ishigh at the top and low at the bottom of the inductor coil, the point ofmaximum flux density in the charge will be relatively high with respectto the osition which it would assume in an .ungra ed coil of the samesize and character. As a result, the stirring in the furnace will bevigorous, and considerable arching of the top of the charge 'will beapparent, as shown from' the elevation of the meniscus 24.

' With a condition of high stirring of this type, very thorough mixingwill take place in the top of the charge, and this portion of the chargewill be readily exposed to the action of the atmosphere or to slaggingreactions, depending upon contact of the slag with the charge. Thus, forexample, carbon could be very advantageously burned off dur ing stirringof this sort.

As seen in Figure 2, the turns are concentrated at the point 23 at ornear the bottom of the coil, while the turns are relatively far apart atthe point 22 at or near the top. Intermediate turns are graded from oneextremity to the other.-

In Figure 2 the effect of the coil will be to lower the point of maximumflux density in the charge with respect to such a point in the samecharacter of coil ungraded. This will operate to reduce the stirring atthe top .of I

the furnace, as seen by the shape of the meniscus 25. The furnace ofFigure 2 would then be desirable to heat a charge which should beprotected from the atmosphere or in which top stirring would beinjurious, as for example a charge containing a high carbon content,where a high carbon content is desired in the final product.

In Figure 3 the coil is graded in both directions from an intermediatepoint 26 of low concentration to extremities 27 and 28 of highconcentration. In this form there will be two points of high fluxdensity, one relatively high and one relatively low in the charge. Theeffect upon the charge is to produce a condition intermediate betweenthose seen in Figures 1 and 2, as shown by the shape of the meniscus 29.Moderate stirring will take place throughout the charge.

In Figures 4 and 5 the faces of the inductor coil turns are at allplaces relatively close together, but the turns are of variant widths,so that at points where high concentration of ampere turns is desiredthe turns will be wound very closely together, and where a lowconcentration iswished for it may also be obtained.

In Figures 4 and 5 the inductor coil is desirably formed of hollowwater-cooled tubing, initially round as seen in 30, and fiattened in adirection parallel to the axis as at intermediate turns between 30 and31 and between 30 and 32 are somewhat less flattened in the respectivedirections. Thus at 32 the ampere turns per unit axial dimension arevery low and at 31 very high.

In general the stirring in Figure 4 Wlll be vigorous as in Figure 1, asshown by the meniscus 24'.

The furnaces of Figures 4 and 5 are provided with heat insulation at 33,and are mounted on bases at 34.

The furnace of Figure 5 has its inductor coil graded in the oppositedirection from that of Figure 4, so that the point of maximum ampereturn concentration will be at the bottom at 31, the point of minimumampere turn concentration at the top at 32 and the intermediate point3.0 will lie between.

Thus the point of maximum flux densitv at the axis will be relativelylow in the coil and there will be little stirring according to theprinciples explained in connection with Figure 2. The meniscus 25' willbe relatively fiat.

It will be obvious that I may grade my inductor coil from the middletoward both extremities as shown in Figure 3, but nevertheless usehollow tubing as shown in Figures 4 and 5. According to the principlesdiscussed this would produce a stirring efl'ect intermed into betweenthose of Figure 4 and Figure 5. This is shown in my copendin'gapplications.

Doubtless the ingenuity of the designer willsua'gest many other ways inwhich inductor coils may be wound to provide variant numbers of turnsper unit axial length at various variously arranged along the coillength, r

without using the forms shown by me in my drawings.

I believe that the use of variant ampere turn concentrations alongdifferent points of 19 the same inductor coil which is carrying the samecurrent throughout is broadly new, and I desire to be protected in theuse of any structure embodying the same to control the stirring in thecharge.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. The method of increasing the normal stirring in an electric inductionfurnace,

20 which consists in'passing an electric current close together at oneend of the coil as compared with the spacing of the turns at the aboutthe charge and increasing the number of ampere turns per unit axialdimension progressively from one end of the section stirred to theother.

'2. The method of increasing the normal stirring in an electricinduction furnace, which consists in passing an electric current aboutthe charge and progressivelyincreasing the number of ampere turns perunit axial dimension about the charge from a minimum about the bottom ofthe charge to a maximum about the top of the charge.

3. The method of decreasing the normal stirring in an electric inductionfurnace, which consists in passing an electric current about the chargeand progressively decreasing the number of ampere turns per unit axialdimension about the charge from a maximum about the bottom of the chargeto a minimum about the top of the charge.

4. In an electric induction furnace, a source of current, an inductorcoil supplied with current from the source, surrounding the charge andhaving its turns relatively other end of the coil.

5. In an electric induction furnace, a source of current, and aninductor coil supplied with current from the source, surrounding thecharge and having the distance between its turns progressivelyincreasing from a minimum about the bottom of the charge to a maximumabout the top of the charge.

6. In an electric. induction furnace, a source of current, and aninductor coil supplied with current from the source, surrounding thecharge and having the spacing of its turns progressively decreased froma maximum about the bottom of the charge to a minimum about the top ofthe charge.

7. In an electric induction furnace, at source of current, and aninductor coil supplied with current from the source, surrounding thecharge and consisting of hollow water cooled tubing edgewo'und about aportion of the charge at one end of the coil and progressively wound andfiat wound toward and at the other end of the coil.

EDWIN FITCH NORTHRUP.

